Isodurene production



D. A. M CAULAY ETAL ISODURENE PRODUCTION Filed Aug. 20, 1954 Nov. 1, 1955 mm SSQQ talk @m i:

INVENTORS:

David A Macaulay y Arf/lur R Lien ATTORBE Y United States Patent ISODURENE PnoDUcrroN David A. McCaulay, Chicago, Ill., and Arthur P. Lien, Highland, Ind., assignors to Standard Oil Company, Chicago, 11]., a corporation of Indiana Application August 20, 1954, Serial No. 451,126

Claims. (Cl. 260-671) This invention relates to the production of isodurene. More particularly the invention relates to the conversion of xylenes to isodurene.

Isodurene (1,2,3,5-tetramethylbenzene) is an exceptionally good blending agent for use in high octane aviation safety fuels. Today, this hydrocarbon is assuming importance as the starting material for the production of intermediates suitable for use in production of high polymers and resins. 1

An object of this invention is the production of isodurene. A particular object is the production of isodurene by a process wherein a xylene or mixture thereof is the starting material. Other objects will become apparent in the course of the detailed description.

The process comprises contacting a hydrocarbon charge, wherein xylene is essentially the only aromatic hydrocarbon present, with sufiicient liquid HF to form a distinct separate acid phase and with a catalytically effective amount of BFz. Substantially anhydrous conditions are maintained throughout the process. A temperature of between about 70 C. and 175 C. is maintained in the xylene contacting zone for a time sufiicient to produce an appreciable amount of mesitylene-the time being between about 2 minutes and 3 hours, the longer times corresponding to the lower temperatures. BF3 is distilled from the acid phase only until about 1 mole of BF; remains per mole of mesitylene produced in the xylene contacting zone. Unconverted xylene and toluene reaction products are removed from the HFBF acid phase by washing with a low boiling non-aromatic hydrocarbon. The washed acid phase is maintained at a temperature between about 70 and 175 C. for a time sufficient to convert an appreciable amount of mesitylene to isodurenea time between about 2 minutes and 2 hours, the longer times corresponding to the lower temperatures. HF and BFa are removed and isodurene is recovered from the reaction product mixture as essentially the only tetramethylbenzene product.

The invention is described in detail in conjunction with the annexed drawing which forms a part of this specification. It is to be understood that the process is not limited to the illustrative embodiment and that many items of process equipment such as pumps, heat exchangers and lines have been omitted from the drawing as these may be readily added by one skilled in the art.

In the drawing, xylene feed from source 11 is passed by way of line 12 into mixer 13. In order to eliminate side reactions, the feed to the process contains xylene as essentially the only aromatic hydrocarbon. The xylenes may be amixture of two or more of the isomers or may be a single xylene isomer. Where the by-products may have some value, small amounts of ethylbenzene may be tolerated in the feed. Although the process is operable in the presence of non-aromatic hydrocarbons, for reasons of capacity and yield, it is preferred to operate with a feed containing little or no non-aromatic hydrocarbons. In any event, it is preferred to operate on a xylene feed such that all of the feed will be taken into the I-IF-BF; acid phase'to form a single essentially homogeneous acid phase. It is possible to attain such a condition with a xylene feed containing up to about 3% of non-aromatic hydrocarbons such as paratfins or cycloparaflins. (The presence of olefins is undesirable because of alkylation 0f the xylene to undesired products.) In view of its relative cheapness with respect to the other xylene isomers, meta-xylene is the preferred xylene charge to the process. In this illustration, the charge consists of essentially pure meta-xylene; the other components are the xylene isomers.

Liquid HP from source 16 is passed by way of line 17 into line 18 and thence into mixer 13. Boron trifluoride is passed from source 21 by way of line 22 into line 18 and thence into mixer 13. In order to avoid hydrate formation and corrosion difficulties, the process is carried out under substantially anhydrous conditions. The liquid HF contains not more than about 3% of water. In this embodiment, the liquid HF consists of commercial grade anhydrous hydrofluoric acid.

Sutficient liquid HF must be present not only to participate in the formation of a complex with the xylenes and other polyalkylbenzenes, but also to dissolve the complex. This amount is readily recognized by the presence of a distinct separate acid phase. More than this amount is desirable. In general, the usage of liquid HP is between at least about 3 moles and 50 moles or more per mole of xylene in the charge. Preferably, the usage of liquid HP is between about 7 and 15 moles per mole of xylene charged to the xylene conversion zone.

At least enough 5P must be present to catalyze the conversion of xylene to mesitylene. More than this amount is desirable since the yield of mesitylene increases with amount of BF; presentup to a point. In order to operate with a single essentially homogeneous acid phase in the xylene contacting zone, it is necessary to use at least about 0.7 mole of BFs per mole of xylene charged. Preferably the usage of BFs is at least 1 mole per mole of xylene charged to the contacting zone. More than this amount may be used, such as 3 moles. In this embodiment, 1.1 moles of BFs are used per mole of xylene charged to mixer 13.

Mixer 13 may be any form of apparatus for contacting liquid HF, BF3 and xylene to provide thorough intermingling and time for the formation of the HFBF3- xylene complex. The complex formation is highly exothermic and in order to control the temperature, mixer 13 is provided with heat exchanger means 24. From mixer 13, the HFBF3 and xylene are passed by way of line 26 into the bottom of reactor 27.

Reactor 27 is shown here as a vertical cylindrical drum provided with motor driven agitation means 28 and a trap out point 29. Any form of vessel which provides the necessary holding time at the desired temperature may be used as a reactor. When operating with the single phase system, external agitation means may be dispensed with. (Sufiicient pressure is maintained on the system to keep the HP in the liquid state and also to keep substantially all the excess BFs dissolved in the acid phase.)

The xylene conversion, i. e., disproportionation to mesitylene, is carried out at a temperature between about C. an about 175 C. The rate of conversation is dependent not only on temperature, but also on time; therefore, suflicient time is allowed to permit the production of an appreciable amount of mesitylene. More than this time is desirable. In general, the xylene conversion is carried on for a time between about 2 minutes and about three (3) hours, the longer times corresponding to the lower temperatures. The preferred temperatures are between about C. and C. At these temperatures, substantially maximum conversion is obtained in times between about minutes and 60 minutes. the longer times corresponding to the lower temperatures.

The xylene conversion results in the production of mesitylene (l,3,5trimethylbenzene) and toluene. The mesitylene forms a complex with HF and BFs which is much more stable than the complex containing xylene. Under these conditions, the toluene product is completely dissolved physically in the acid phase. At the completion of the conversion time, the acid phase is Withdrawn from reactor 27 by way of valved line 31 and is passed into flash drum 32. Flash drum 32 is a vessel constructed to permit the withdrawal of BF3 and some HF overhead as gases. In order to accomplish this, the pressure in flash drum 32 is somewhat lower than that in reactor 27. SP3 gas and HF vapor are taken overhead by way of line 33 and are recycled by way of lines 34 and 18 to mixer 13. In flash drum 32, enough BFa is distilled to reduce the BF: content of the acid phase to about 1 mole per mole of mesitylene contained therein. Under these conditions, practically all of the xylene will exist in the acid phase in the uncomplexed state, i. e., be dissolved in physical solution. Thus, after BF: has been distilled, only about 1 mole of BFa per mole of mesitylene present will exist in flash drum 32. There will also exist in flash drum 32 liquid HF, HF-BF3 mesitylene complex, probably some HF-BFa xylene complex, toluene and xylene in physical solution in the acid phase and possibly a separate phase of toluene and xylene.

A bottoms is withdrawn from flash drum 32 and is introduced by way of line 37 into extraction tower 38. Extractor 38, in this embodiment, is a vessel adapted for the continuous countercurrent contacting of two immiscible fluids. Instead of a single tower a series of vessels may be used, such as is readily determined by one skilled in the art. Near the lower end of extractor 38 hexane is introduced from source 41 by way of lines 42 and 43. The uncomplexed hydrocarbons may be removed from the acid phase by contacting with any immiscible liquid which is a solvent for said uncomplexed hydrocarbons. In order to simplify the problem of separating the wash liquid from the aromatic hydrocarbons, a low boiling non-aromatic hydrocarbon is the preferred extracting medium. Examples of such hydrocarbons are pentane, hexane and cyclopentane.

The presence of xylene in the acid phase has an adverse eflect on the conversion of mesitylene to isodurene. Therefore, it is desirable to reduce the amount of xylene present in the acid phase and preferably to substantially eliminate the xylene from the acid phase. Sutlicient low boiling non-aromatic hydrocarbon is used to substantially reduce the amount of uncomplexed hydrocarbons, i. e., toluene and xylene and some mesitylene in the acid phase. About 1 volume of wash hydrocarbon is needed per volume of hydrocarbon to be removed from the acid phase in order to substantially reduce the uncomplexed hydrocarbons. In order to substantially eliminate the uncomplexed hydrocarbons, between about 200% and 400% of wash hydrocarbon should be used, based on the uncomplexed hydrocarbons, under eflicient contacting conditions. In this embodiment, 300 volume percent of hexane was introduced by way of line 43 into extractor 38.

From an upper portion of extractor 38 there is withdrawn a separate phase comprising non-aromatic hydrocarbons, which phase is introduced by way of line 44 into fractionator 46. In order to economize on heat, extractor 38 is operated at about the temperature present in reactor 27. At this elevated temperature even the HF-BF3 mesitylene complex is appreciably disassociated so that mesitylene is present in the acid phase in the uncomplexed condition and some mesitylene will be extracted from the acid phase by the Wash hydrocarbon. Fractionator 46 is schematically shown and is provided with heat exchanger 47. Hexane is withdrawn overhead, condensed in an exchanger not shown and recycled by way of line 43 to extractor 38. Toluene is withdrawn by way of line 49 and is sent to storage not shown. The toluene produced is nitration grade and may be used wherever essentially pure toluene is necessary. The xylene fraction is withdrawn by way of line 51 and is recycled by way of lines 52 and 12 to mixer 13. A bettoms fraction of mesitylene is withdrawn by way of valved line 54.

The washed acid phase is withdrawn from extractor 38 by way of line 56. This washed acid phase comprises HF, SP3 and mesitylene; it also contains some xylene, toluene and hexane. The mesitylene from fractionator 46 and line 54 is introduced by way of line 57 into line 56.

In order to maximize the yield of the desired isodurene in the mesitylene conversion zone, at least 1 mole of BF; is present per mole of mesitylene in the acid phase. And preferably at least 1 mole per mole of polyalkylbenzene is present. Therefore, additional BF; is introduced from source 61 by way of valved line 62 into line 63 where it meets the acid phase from line 56 and the mesitylene from line 57. If necessary, additional HF may be introduced into line 63 from source 66 by way of valved line 67. In this illustration, sutficient HF is introduced to have in the mesitylene conversion zone 10 moles of liquid HF per mole of mestitylene present.

The contents of line 63 are introduced into reactor 71 which is similar in construction to reactor 27. Reactor 71 is provided with motor driven agitator means 72 and trap out 73. The mesitylene conversion reaction, i. e., disproportionation, produces isodurene and metaxylene. The mesitylene conversion zone is maintained at a temperature between about 70 C. and 175 C. for a time sufficient to produce at least an appreciable amount of mesitylene. Operation at these temperatures for a time between about 2 minutes and two (2) hours, the longer times corresponding to the lower temperatures results in substantially maximum yields. It is preferred to operate at a temperature between about C. and C. for a time between about 5 minutes and 15 minutes, the longer times corresponding to the lower temperatures. In this embodiment, reactor 71 is operatedat a temperature of 100 C. for a time of 10 minutes.

The acid phase containing isodurene, unreacted mesity-- lene, xylene and toluene is withdrawn from reactor 71 by way of line 76 and is introduced into decomposer 77 which is provided with heat exchanger 78. In decomposer 77, the HF and BF are distillatively removed from the acid phase. This may be accomplished-either by operating the decomposer at subatrnospheric pressures or by raising the temperature. The temperature of operation of decomposer 77 should not be so high that side reactions occur during the HF and BF: removal.

A suitable temperature of operation is about C.

The HF and BE: are taken overhead and are recycled by way of lines 79, 34 and 18 to mixer 13. In this embodiment, decomposer 77 is operated to remove hexane from the reaction product mixture by way of line 81. This hexane fraction may be recycled for reuse in extractor 38 by way of lines not shown.

The reaction product mixture of aromatic hydrocarbons is withdrawn from decomposer 77 by way of line 83 and is introduced into fractionator 84 which is provided with reboiler 86. Fractionator 84 is shown schematically in this illustration. The reaction product mixture is distillatively fractionated into a toluene fraction which is withdrawn by way of line 88 to storage not shown. A xylene fraction is withdrawn and recycled by way of lines 89,.- 52 and 12 to mixer- 13. This xylene fraction is essentially pure meta-xylene, even when the charge from source 11 contains ortho and para-xylene isomers. A mesitylene fraction is withdrawn and re cycled by way of lines 91, 57 and 63 to reactor 71-.

The tetramethylbenzene fraction consists of essentially only isodurene. This isodurene product is withdrawn by way of line 93 to storage not shown. Under so'm'e' con-" containing a trace amount of pseudo cumene.

ILLUSTRATIVE RESULTS methylbenzenes containing more than 3 methyl groups were found in the reaction product mixture.

Test No. 2 was carried out using mesitylene as the charge in the presence of 1 mole of BF: per mole of mesitylene. The conversion was carried out at 80 C. for a time of 30 minutes. Although this run was carried out at a much lower temperature than Run No. 1, the reaction product mixture contained not only tetramethylbenzene, but also pentamethylbenzene. The tetramethylbenzene was, within the error of infrared spectrometry, 100% isodurcne.

Run No. 3 was carried out to show the effect of contacting the acid phase with a paraflinic hydrocarbon. In this run, meta-xylene was contacted with liquid HF and In rd r to ShOW that the Sequence of Operations Set 0.87 mole of BFs per mole of xylene at 122 C. for 30 out in the foregoing description of the process are necesi t Th reactor a the ool d t 7 C, To th sary for the production of substantial amounts of isoooled reactor 1.91 moles of n-heptane were charged durene starting with xylene as the original feed, certain and the acid phase and n-heptane agitated. The conillustrative experiments are set out below. These experit t f th reactor were ermitted to ettle for 10 minments were carried out using a 1570 ml. carbon steel ret a d the the two phases contained therein were actor provided with a 1725 R. P. M. mechanical stirrer. withdrawn into separate vessels containing crushed ice. In the experiments, the desired amount of hydrocarbon The n-heptane was removed from the rafiinate phase and Was charged to the Thactof; Commercial grade nhydrous the rafiinate aromatic hydrocarbons were separated as liquid HF was then added; and ER was added to the described above. The aromatic hydrocarbons were remixture of liquid HF and hydrocarbon. The reactor covered from the acid phase and analyzed as described was maintained at the desired temperature of operation above. Even though, theoretically, enough BFs was for a particular time. The contents of the reactor were present to complex all the polymethylbenzene present cooled to room temperature of about 20 C. and were in the reactor prior to heptane addition, the heptane then withdrawn into a vessel filled with crushed ice which under these washing conditions removed about onewas brought to the temperature of a Dry Ice-acetone 3 quarter of the xylene from the acid phase into the sepbath. The hydrocarbons separated as an upper oil layer arate hydrocarbon phase. About one-half of the toluene above a lower aqueous acid layer. The oil layer was produced in the conversion was taken into the separate withdrawn, neutralized with aqueous ammonia and water hydrocarbon phase. The difference in stability of the Washed. The washed hydrocarbons were carefully fracxylene complex and the mesitylene complex is illustrated tionated in a column providing about theoretical by the absence of mesitylene from the rafiinate phase. plates. Close boiling fractions from the distillation were Even though the temperature was much higher than that analyzed by ultraviolet and infrared spectrometry as well of Run No. 1 and much more BF; was present, no tetraas by physical characteristics. (Deviations from the methylbenzene was produced in this run wherein Xylene above procedure are described in the individual experiwas charged. This run further accentuates the peculiarity ments.) The results of these experiments are shown in of the disproportionation of mesitylene wherein at some the table. 40 C. lower temperature not only was the next higher Table l Run N0 1 2 3 4 5 Feed n-xylene... mesitylene.. m-xylene. Mol 2.42. Wash Hydrocarbon n-heptane Moles 1.54. Temperature, C. 120. Time, Minutes 30. HF, moles 22.0. BFs, moles. 2.03.

HF/Feed, mole ratio. BFz/Feed, mole ratio Rafli- Acid Rafli- Acid Ratfi- Acid nate Phase Total nate Phase Total nate Phase Total Aromatic Reaction Product:

Distribution, wt. percent 23 77 100 15 85 100 24 76 100 Composition, mole percent Benzene. 0 0 0 0 0 0 4 0 1 Toluene 76 22 36 20 28 62 19 30 Xylene. 24 27 26 30 12 15 34 16 20 Trimeth 0 51 38 0 57 48 0 47 36 Tetramethylbenzene 0 0 0 0 11 9 0 7 5 Higher methylbenzenes 0 0 0 0 0 0 0 Other products 0 0 0 0 0 0 0 0 B 11 8 e Mesitylene except for trace of pseudocumene. b 100% 1,2,3,5-tetramethylbenzene. s 100% pentamethylbenzene.

d Heptane added to reactor after cgnversion time and cooling to 7 0.

e Acid phase aromatics from Exp. I Added to reactor at start of conversion period. I Higher boiling resulting from alkylation from heptane cracking.

ture contained only toluene, meta-xylene and trimethyl- The trimethylbenzene product was mesitylene No polybenzene.

methylbenzene produced, i. e., tetramethylbenzene, but also an appreciable amount of the pentamethylbenzene was produced. Apparently, some considerable difference in ease of disproportionation, heretofore unsuspected, exists between xylene and mesitylene.

Run No. 4 was carried out using an aliquot portion of the aromatic reaction product recovered from the separate acid phase of Run No. 3. That is, the charge to Run No. 4 was a mixture of toluene, meta-xylene and mesitylene. This feed was contacted with liquid HF and 1.37 moles of BF3 per total aromatics in the feed at a temperature of 121 C. for a time of 20 minutes. The reactor was then cooled to 7 C. and contacted with nhepta'ne in a manner identical with that of Run No. 3. The separate hydrocarbon and acid phases were recovered arid the aromatic hydrocarbons analyzed. Once again, despite the large excess of BF3, a large amount of meta-xylene was taken into the hydrocarbon phase. None of the mesitylene or isodurene product was removed from the acid phase. The total product distribution shows a goodly amount of isodurene was produced even though a considerable amount of xylene was present in the reaction zone. This run indicates that it is possible to obtain isodurene by the conversion of mesitylene in the presence of considerable amounts of xylene and toluene. The results of Run No. 2 show that it is much to be preferred that essentially pure mesitylene be the charge to the mesitylene conversion zone. It is of int'eres't that under the conditions of Run No. 4 no methylbenzenes containing more than 4 methyl groups were produced. Thus, it is believed that not only does the presence of the xylene interfere with the disproportionation of mesitylene to isodurene, but also interferes with further disproportionation to pentamethylbenzene.

Run No. 5 was carried out to determine the eifect of the presence of a paraffinic hydrocarbon in the conversion zone during the conversion reaction. In Run No. 5 meta-Xylene and n-heptane were contacted with liquid HF and BF:; at 120 C. for 30 minutes. Two distinct phases were found to be present in the reactor when the contents were removed. Analysis of the heptane-free reaction products showed that a considerable amount of cracking had taken place, which cracking had resulted in the production of a considerable amount of material higher boiling than pentamethylbenzene. In addition to production of a large amount of mesitylene, an appreciable amount of material boiling over the tetramethylbenzene and pentamethylbenzene range was found, which material is believed to be a mixture of hydrocarbons, probably alkylbenzenes from the alkylation of aromatics with fragments derived from the heptane cracking. This test indicates that the xylene conversion reaction and the mesitylene conversion reactions are desirably carried out in the absence of any significant amount of paraffinic hydrocarbons.

The above experimental results clearly show that it is not practical to attempt to obtain tetramethylbenzenes by the direct disproportionation of xylene in the presence of liquid HF and BFs. This shows that a two-step operation wherein xylene is converted to mesitylene in a first step and then, to obtain high yield of isodurene, a xylenedenuded phase containing mesitylene is reacted to obtain the desired isodurene product.

Thus having described the invention, what is claimed is:

l. A process for the production of isodurene which comprises (1) contacting, under substantially anhydrous conditions, xylene as essentially the only aromatic hydrocarbon, liquid HF in an amount of at least about 3 moles per mole of xylene, and a catalytically effective amount of BB, at a temperature between about 70 C. and 175 C. for a time between about 2 minutes and 3 hours, the longer times corresponding to the lower temperatures, (2) distilling ofi BF: until only about 1 mole of BF: remains in the acid phase per mole of mesitylene produced in zone (1), (3) washing the acid phase of (1) with a low boiling non-aromatic hydrocarbon in an amount sufficient to substantially reduce the quantity of uncomplexed aromatic hydrocarbons dissolved in said acid phase (4) separating a phase comprising non-aromatic hydrocarbons from an acid phase comprising HF, BF3 and mesitylene, (5) maintaining the acid phase of (4) at a temperature between about C. and 175 C. for a time between about 2 minutes and 2 hours, the longer times corresponding to the lower temperatures, to convert mesitylene to isodurene, (6) removing HF and BF3 to recover a hydrocarbon reaction product mixture containing isodurene as essentially the only tetramethylbenzene, and (7) recovering isodurene from said product mixture.

2'. The process of claim 1 wherein the hydrocarbon charge is substantially pure xylene.

3. The process of claim 2, wherein said xylene is metaxylene.

4. The process of claim 1 wherein the BF3 usage is at least about 0.7 moles per mole of xylene.

5. The process of claim 1 wherein the wash hydrocarbon usage is between about 200% and 400% of the amount of uncomplexed hydrocarbon in said acid phase and the washing is elfected under conditions to remove substantially all of the uncomplexed hydrocarbons from said acid phase.

6. The process of claim 5 wherein said wash hydrocarbon is hexane.

7. A process for the production of isodurene, which process comprises (A) contacting, under substantially anhydrous conditions, a feed consisting essentially of at least 1 xylene isomer with between about 7 and 15 moles of liquid HF and at least about 1 mole of BF3, respectively, per mole of xylene, at a temperature between about and C. for a time between about 10 minutes and 1 hour, the longer times corresponding to the lower temperatures, (B) distilling BF; from the acid phase until said acid phase contains about 1 mole of BF per mole of mesitylene present in said acid phase, (C) washing the acid phase of (B) with a low boiling parafiinic hydrocarbon in an amount between about 200% and 400% based on uncomplexed aromatic hydrocarbons present in the acid phase under conditions to remove substantially all of said uncomplexed hydrocarbons, (D) separating a phase comprising parafiinic hydrocarbon and extracted aromatic hydrocarbons from an acid phase comprising HF, BFa, and mesitylene, (E) maintaining the acid phase of (D) at a temperature between about 85 and 120 C. for a time between about 5 minutes and 15 minutes, the longer times corresponding to the lower temperatures in order to produce isodurene from mesitylene, (F) removing HF and BF3 from the isodurenecontaining acid phase to obtain a hydrocarbon reaction product mixture containing isodurene as essentially the only tetramethylbenzene, and (G) recovering essentially pure isodurene from said product mixture.

8. The process of claim 7 wherein the paraffinic hydrocarbon phase of (D) is distilled to recover toluene, xylene, mesitylene and said xylene and mesitylene are recycled to the xylene conversion zone (A) and mesitylene conversion zone (E), respectively.

9. The process of claim 8 wherein xylene and mesitylene distilled from said hydrocarbon reaction product mixture are recycled to the xylene conversion zone (A) and the mesitylene conversion zone (E), respectively.

10. The process of claim 7 wherein said paraffinic hydrocarbon is hexane.

No references cited. 

1. A PROCESS FOR THE PRODUCTION OFISODURENE WHICH COMPRISES (1) CONTACTING, UNDER SUBSTANTIALLY ANHYDROUS CONDITIONS, XYLENE AS ESSENTIALLY THE ONLY AROMATIC HYDROCARBON, LIQUID HF IN AN AMOUNT OF AT LEAST ABOUT 3 MOLES PER MOLE OF XYLENE, AND A CATALYTICALLY EFFECTIVE AMOUNT OF BF3, AT A TEMPERATURE BETWEEN ABOUT 70* C. AND 175* C. FOR A TIME BETWEEN ABOUT 2 MINUTES AND 3 HOURS, THE LONGER TIMES CORRESPONDING TO THE LOWER TEMPERATURES, (2) DISTILLING OFF BF3 UNTIL ONLY ABOUT 1 MOLE OF BF3 REMAINS IN THE ACID PHASE PER MOLE OF MESITYLENE PRODUCED IN ZONE (1), (3) WASHING THE ACID PHASE OF (1) WITH A LOW BOILING NON-AROMATIC HYDROCARBON IN AN AMOUNT SUFFICIENT TO SUBSTANTIALLY REDUCE THE QUANTITY OF UNCOMPLEXED AROMATIC HYDROCARBONS DISSOLVED IN SAID ACID PHASE (4) SEPARATING A PHASE COMPRISING NON-AROMATIC HYDROCARBONS FROM AN ACID PHASE COMPRISING HF, BF3 AND MESITYLENE, (5) MAINTAINING THE ACID PHASE OF (4) AT A TEMPERATURE BETWEEN ABOUT 70* C. AND 175* C. FOR A TIME BETWEEN ABOUT 2 MINUTES AND 2 HOURS, THE LONGER TIMES CORRESPONDING TO THE LOWER TEMPERATURES, TO CONVERT MESITYLENE TO ISODURENE, (6) REMOVING HF AND BF3 TO RECOVER A HYDROCARBON REACTION PRODUCT MIXTURE CONTAINING ISODURENE AS ESSENTIALLY THE ONLY TETRAMETHYLBENZENE, AND (7) RECOVERING ISODURENE FROM SAID PRODUCT MIXTURE. 